Plastic containers are ubiquitous. They are manufactured for distributing and selling milk, juice, soda, and other products as well as for ornamental consumer products. Blow molding is the primary manufacturing process for forming beverage containers. An aluninum mold is used which includes a mold body block and a removable neck block for forming the top (sometimes threaded) portion of the container. The neck block is removable from the mold body block since one user may desire a screw cap, another a snap screw cap, while another may want a snap cap and each type of cap requires a different kind of neck block.
Each half of the mold is mounted to a back plate which in turn is mounted to the platen of the blow mold machine. The opposing platens are driven towards each other bringing each half of the mold together. A tube of plastic called a parison is then extruded between the mold halves and then blown out into the mold to form a container. The platens are then drawn apart and the container is removed from the mold, trimmed, and inspected for quality. There may be one to as many as six or more molds per blow machine and the blow machine cycles as often as every six seconds producing up to approximately six hundred containers in an hour.
Sometimes, the neck blocks are not manufactured to the same dimensions as the mold body blocks. Also, the aluminum molds wear and when they do, they must be refurbished. The neck blocks are removed and, after refurbishing (removing material) the mold, the neck block is remounted to the refurbished mold body block. This assembly is then mounted to the back plate and the neck block must be carefully aligned with respect to the mold body block. To accomplish this, sometimes shims are placed under the mold body block to adjust the difference in heights between the standard neck block and the refurbished mold body block. As much as 0.0005" misalignment between the neck block and the mold body block can severely affect quality. Manual shimming of the neck block is time consuming, labor intensive and often unreliable. If the neck block is not correctly aligned with respect to the mold body block, trimming flash from the container can become difficult if not impossible. In most cases, the neck block becomes too large for the refurbished body block. In this situation, shims won't work since the neck block actually needs to be set back on or into the back plate. This would require machining the neck block which is impractical in light of its interchangable value, or alternatively, machining the individual back plate which is also impractical because of the labor required.
Moreover, each half of the mold must be vertically aligned to precisely mate with the other half when the molds are brought together. Also, vertical alignment is necessary to align the molds with the blowing nozzle or blow pin of the blow machine.
Remarkably, this is often accomplished by snugly securing the back plate to the platen with the mold attached and then striking the back plate in the direction the mold is needed to be moved. The mold is visually positioned and then the back plate is torqued to the platen. This can damage the back plate and often results in misalignment between the molds halves.
Accordingly, manually aligning the neck block with respect to the body block of the mold and vertically aligning the mold halves on the platens is a time consuming and imprecise process.